L.K. Malhotra

Electrical, optical and annealing characteristics of ZnO:Al films prepared by spray pyrolysis☆

Abstract Transparent conducting thin films of aluminium-doped zinc oxide have been prepared by spray pyrolysing a solution of zinc acetate and aluminium chloride. The effect of changing the aluminium-to-zinc ratio from 0 to 6 at.%, substrate temperature from 300 to 500 °C and spray rate from 5 to 16 ml min −1 has been thoroughly investigated. As-deposited films have very high resistivity and high visible transmission. Annealing of the as-deposited film in a hydrogen atmosphere leads to a substantial reduction in resistivity without affecting the optical transmission. The best films have a resistivity of about 10 −3 ω cm and a visible transmission of about 85%. Preliminary studies indicate that the films are stable in silane and silane plus hydrogen plasma.

Sol gel deposition of pure and antimony doped tin dioxide thin films by non alkoxide precursors

Pure and antimony doped tin oxide films have been deposited by the alcoholic sol gel method using non alkoxide precursor-SnCI2.2H20 as host and SbCI3 as the dopant precursor. Using the dip coating method, thin films of thickness up to 300 nm have been uniformly deposited on coming 7059, KBr and Silicon substrates. The influence of various paratneters such as viscosity and pH of the sol; pulling speed and sintering temperature on thickness of the coatings and their microstructure have been investigated. Pure as deposited films have a visible transmission of (83%) but very high resistivity (7. I X 10-2 fl-m). Doping and annealing treatments bring it down to about 5 × 10- ~ l)-m. It has been possible to obtain antimony doped tin oxide films having a sheet resistance of 5 fl/r-l and a visible transmission of 80% after annealing treatment by hydrogen plasma.

Effect of palladium cap layer thickness on desorption of hydrogen from PrHx films: A spectroscopic ellipsometry study

Optical characterization of palladium (Pd) capped PrHx films has been performed using phase modulated spectroscopic ellipsometry to study the effect of thickness of a cap layer on the deloading of hydrogen from the capped hydride films. Experimental Ψ and Δ spectra have been fitted to an optical model consisting of an air/Pd/PrHx/glass substrate. The direct band gap of the PrHx films, calculated from the Tauc plots of these films, has been found to decrease with an increase in the thickness of the Pd overlayer, which in fact is due to enhanced deloading of hydrogen. The removal of hydrogen from PrHx films leads to the formation of localized states, whose signature is clearly observed in the Tauc plots. The energy corresponding to a transition involving these states and the conduction band has been found to increase with increasing Pd overlayer thickness.

On the origin of photocontraction effect in amorphous chalcogenide films

Large photocontraction of up to 26% has been observed in some chalcogenide films. Conditions necessary for the occurrence of large photocontraction are indicated to be: ability to form a glass, high bond ionicity, strong electron-phonon coupling, low density of the bulk material, and a large density difference between the bulk and the thin-film. These studies suggest that contraction (densification) is due to the mechanical collapse of the columns resulting from the large internal stresses caused by the interaction of the photogenerated carriers and the charged dangling bonds.

High energy heavy ion induced changes in the photoluminescence and chemical composition of porous silicon

Abstract Anodically etched porous silicon samples have been irradiated with 85 MeV Ni ions. The ion irradiation results in a complete suppression of the major photoluminescence peak at 697 nm and the shoulder peak at 6.7 nm. In the ion-irradiated sample, the weak Pl peak, appears at 588 nm. Elastic recoil detection analysis has been used to study the changes in the hydrogen concentration profiles during ion irradiation. Infrared spectroscopy has been employed to investigate the effect of ion irradiation on the chemical species present in the porous silicon. The changes in the photoluminescence spectra have been correlated with the resulting changes in the concentration of hydrogen and chemical complexes containing Si, H and O in the porous silicon sample on irradiation.

Electrical, optical, and structural properties of reactive ion beam sputtered hydrogenated amorphous germanium (a‐Ge:H) films

Electrical, optical, and structural properties of hydrogenated amorphous germanium (a‐Ge:H) films prepared by reactive ion beam sputtering of a high‐purity crystalline germanium target under varying deposition conditions have been studied. A detailed description of the deposition setup, preparation procedures, and techniques of property measurement is given. The dependencies on beam voltage, H2:Ar flow ratio, and substrate temperature of the room‐temperature dark conductivity, optical band gap, hydrogen content, and ellipsometric and IR data are reported and analyzed. The minimum conductivity (10−4 Ω−1 cm−1) a‐Ge:H films have been obtained for H2:Ar flow ratio of 16:1, and beam voltage and substrate temperature of 1000 V and 250 °C, respectively. These films contain a hydrogen concentration of about 11 at. % and show an optical band gap near 1.04 eV. The IR spectra reveal absorption bands corresponding to both monohydride (Ge‐H) and dihydride (GeH2) groups for all the samples deposited. The monohydride ab...

Electrical and optical properties of hydrogenated amorphous silicon‐germanium (a‐Si1−xGex:H) films prepared by reactive ion beam sputtering

Thin films of hydrogenated amorphous silicon‐germanium (a‐Si1−xGex: H) alloys have been prepared by reactive ion beam sputtering of a composite target of silicon and germanium. The dependence of the deposition rate, conductivity‐temperature variation, optical absorption coefficient, refractive index, imaginary part of the dielectric constant, hydrogen content, and infrared (IR) absorption spectra on germanium content (x) are reported and analyzed. For a typical composition—a‐Si28Ge72:H (x=0.72), the effect of beam voltage, H2:Ar flow ratio, and substrate temperature on the material properties have also been investigated. For the films prepared with increasing x, the expected behavior of a decrease in both hydrogen content and band gap and an increase in the electrical conductivity have been observed. The films prepared at x>0.80 are found to be more homogeneous than the films deposited at 0.0<x<0.80, due to the compositional disorder introduced by the random mixing of Si and Ge atoms in the a‐Si1−xGex: H ...

GaGeTe films as phase-change optical recording media

Abstract Ga 20 Ge 30 Te 50 thin films deposited by vacuum evaporation on various substrates have been studied for their structural and optical properties. The as-deposited amorphous films were crystallized by thermally annealing them. The optical constants of the amorphous films indicate semiconducting behaviour ( n > k ). The optical bandgap ( E g ) determined from Taucs plot is 0.7 eV. The change in reflectance on crystallization has been utilized to obtain maximum optical contrast by optimising the thickness of the film.

Spectrally selective surfaces on stainless steel produced by chemical conversion

Abstract Solar selective coatings on stainless steel, stable up to 200 °C, were prepared by chemical conversion. The coatings had an integrated absorptance α of about 0.91 and a hemispherical thermal emittance e 100 of about 0.12. Compositional analysis revealed that these coatings consisted of a mixture of Fe 2 O 3 , Cr 2 O 3 and elemental iron graded towards the substrate. The absorption seems to be partly due to interference effects and partly due to metallic particles dispersed in a semiconducting Fe 2 O 3 -Cr 2 O 3 matrix. The degradation of coatings above 200 °C was found to be due to the increase in thickness of the oxide layer and to the absence of elemental iron.

Photodensification in amorphous PSe thin films

Abstract The photoinduced shift in the absorption edge, changes in optical constants, film thickness contraction and rate of chemical dissolution were investigated for PSe thin films deposited under normal (0°) and oblique (80°) incidence. These studies confirm our view that a variety of photoinduced phenomena observed earlier in germanium- and arsenic-based chalcogenides are primarily due to the chalcogen sulphur and/or selenium and that the role of germanium, arsenic or phosphorus is to act as matrices to stabilize a low density glassy structure. An irreversible thickness contraction of about 5% was found in films of P4Se10 deposited at 80° and is due to the decrease in the void volume on band gap irradiation. The thickness contraction was used for the generation of high resolution relief patterns. Photoinduced effects on the wet and dry etching behaviour of films, with and without an overlayer of silver, suggest the suitability of these films for positive and negative resist applications. Typical values of the contrast and the sensitivity for positive resist application are 2.6 and 1023 photons m−2 respectively.